Preheat oven to 400°. Line a large baking sheet with foil and lay the potatoes on top. Pierce all over with a fork, then rub the potatoes all over with olive oil and season with salt and pepper. Bake until the skin is crispy and the potato is tender, about 1 hour. Let cool slightly until cool enough to handle.

Meanwhile, make filling: Heat a large skillet over medium-high heat, then add ground beef. Season with garlic powder, cayenne, salt and pepper, and cook until the ground beef is no longer pink. Drain fat.

Make sauce: In a small bowl, whisk together mayonnaise, mustard, ketchup, vinegar and paprika until smooth.

When the potatoes are cool enough to handle, cut them in half lengthwise. Scoop out the flesh with a spoon, leaving a ¼ thick inch by the skin. Return the potatoes, cut side-up, to the baking sheet and brush with melted butter. Top with cooked ground beef, shredded cheddar, and sesame seeds. Broil until the cheese is bubbling, about 3 minutes.

Transfer skins to a server platter and top with chopped tomatoes, lettuce, and pickle relish. Drizzle with sauce and serve warm.